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One body is reported to have been recovered after a Tongan ferry sunk with 79 people on board.
New Zealand's Rescue Coordination Centre is conducting the search.
A spokeswoman said a crew member in a Royal New Zealand Air Force Orion reported seeing a body recovered by a vessel in the search area, but that has not been confirmed by Tongan police.
The Orion arrived at first light to begin the search.
A life raft and more than 20 people are still missing, while 53 others have been rescued.
A mayday call was picked up in New Zealand from the inter-island ferry Princess Ashika just before 11pm, said RCCNZ spokesman Ross Henderson.
A few minutes later, the centre received a distress beacon alert from the vessel, which was heading from Nuku'alofa to Ha'afeva, in the Nomuka Islands group.
By midday today, the Orion had covered nearly half of the 207sq km search area, pinpointing the sinking location about 86km northeast of Nuku'alofa.
A second Orion is due to take over this afternoon.
The crew reported good search conditions and a trail of debris from the sunken vessel stretching about 15km.
The first boats to reach the scene pulled 42 people from liferafts - 17 passengers and 25 crew, including the captain.
Another 11 were subsequently found safe and well this morning.
Survivors are being taken by boat to Ha'feva, where RCCNZ is working with Tongan authorities to arrange onshore assistance.
Three boats, including the Tongan Navy vessel Pangai, were still helping with the search, with a fourth vessel due to join them early this afternoon.
A balmy water temperature of 25 degrees would aid the survival chances of those still in the water, said Maritime New Zealand spokesman Neville Blackmore.
A two- to three-metre swell is forecast to ease during the day.
It was not yet known what caused the sudden sinking of the ferry which was carrying 10 tonnes of cargo, some of which was believed to be timber.
Maritime New Zealand spokesman Ross Henderson said survivors may be clinging to the timber.
The Princess Ashika, built in Japan in 1970, had only been plying Tongan waters for a few weeks and was just a stop-gap measure ahead of a new ferry coming into service.
- NZPA, NEWSTALK ZB AND NZHERALD STAFF
